## Description
Makes AWS Bedrock credentials optional. When `AccessKey` and
`AccessKeySecret` are not set, AI Bridge falls back to the AWS SDK
default credential chain, which supports IAM Roles (instance profiles,
IRSA, ECS task roles), SSO, shared credentials files, and environment
variables.
This allows AI Bridge to authenticate with AWS Bedrock using:
- Permanent credentials (access key + secret) as before
- IAM Roles, shared config files, environment variables, SSO, etc, via
the SDK default credential chain
Depends on: https://github.com/coder/aibridge/pull/265
Related to: https://github.com/coder/aibridge/issues/144
Related to: https://linear.app/codercom/issue/AIGOV-67
_Disclaimer: initially produced by Claude Opus 4.6, modified and
reviewed by @ssncferreira ._
Susana Ferreira
522118ab20